We are conducting a cross-sectional, case-controlled study of energy expenditure in subjects with narcolepsy, who will be individually matched with healthy controls. The primary objectives of this study is to determine whether hypocretin-deficient subjects with narcolepsy have lower energy expenditure as determined by a 24h stay in the metabolic chamber. During an inpatient visit of approximately 3-4 weeks following screening and medication washout the following additional parameters will be assessed: physical activity (by doubly labeled water study and activity monitors); food intake (dietary history, experimental in-house buffet and food vending machines with computerized access code), body composition (dexa measurements and abdomen CT); measurements of cutaneous and core body temperature and heart rate variability, both indirect indices of autonomic nervous system activity. Endocrine in-depth characterization will include insulin resistance (oral and iv glucose tolerance test), leptin and gh-relin levels as well as characterization of the main neuroendocrine axes.